As is known, silencers of exhaust systems of motor vehicles define a stretch of the exhaust path along which the noise produced by the pressure waves of the exhaust gases emitted by the engine is attenuated. The silencer typically comprises an outer metal containment, shell or casing, one or more metal ducts and/or diaphragms set within the casing, and traversed, in use, by the exhaust gases, and an insert made of sound-deadening material, typically mineral fibres, which is set in the free cavities of the casing in such a way as to fill the internal space thereof and coat/envelop the ducts and/or diaphragms so as to attenuate the transmission of the noise generated by the gases outwards.
Some types of silencers sound-deadening inserts comprise fibreglass mattresses, which are obtained through methods that basically envisage winding one or more fibreglass threads around a tubular element so as to obtain a tubular skein, flattening the skein of fibres so as to obtain the mattress of reduced thickness, and making stitches using thread on the fibreglass mattress so as to prevent the mattress from opening up when it is being installed inside the silencer casing.
Making stitches using thread on the fibreglass mattress envisaged in the methods described above, even though effective, is particularly inconvenient in so far as it has a major effect on the overall times and costs necessary for producing the insert.
The present applicant has consequently conducted an in-depth study having the purpose of identifying a solution that would specifically enable the aim to be achieved of providing a method and a machine for producing an insert, made of sound-deadening material that is without stitches, but presents a certain degree of compactness, and is consequently not subject to opening when it is being moved and in the course of its installation in the casing of the silencer.